Anatomic details of the infantile oropharynx and relationships to possible airway obstruction in sudden infant death syndrome (SIDS) are understood incompletely. Tonkin recognized this in 1975, suggesting that enlargement of the tongue might be important in SIDS, within the context of other anatomic and physiologic factors unique to early life. We therefore conducted a morphometric study of the tongue in 100 victims of SIDS and 36 control infants; the latter group consisted of infants with the same range in age and body size who had grown normally and died acutely. Highly significant differences in tongue weight, width, and thickness were demonstrated between the two groups by linear regression and analysis of covariance. Two multivariate techniques, stepwise discriminant analysis and factor analysis, identified marked discordance between somatic and lingual size in SIDS and a statistical uniqueness in tongue thickness. Certain explanations for lingual enlargement in SIDS were ruled out: redistribution of fluid and other effects of death, postmortem interval, duration and mode of feeding, and smallness of control tongues. At present, the functional significance of these observations is unclear. The effects of both normal and increased tongue size on airway patency are, however, widely recognized. Further studies of the enlarged tongue, addressing such topics as in situ anatomy and developmental mechanisms, are necessary to establish the potential for pathophysiologic consequences in SIDS.